1. Field of the Invention
The present invention relates to polymerization catalysts which are suitable for preparing polymers of oxirane compounds such as ethylene oxide, epichlorohydrin and allyl glycidyl ether by suspension precipitation polymerization and to a process for preparing polymers of oxirane compounds using the polymerization catalysts.
2. Description of the Prior Art
Since polymers of oxirane compounds having various properties can be obtained by using a variety of oxirane compounds as a starting material, the polymers are used in very wide fields such as rubber parts for automobiles, rubber members for electrical and electronic equipments, polymers for various plastics blending and solid polyelectolytes.
Industrial processes for preparing the polymers of oxirane compounds are exemplified by solution polymerization wherein the oxirane compounds are polymerized in an organic solvent which can dissolve monomers and the polymers and by suspension precipitation polymerization wherein the oxirane compounds are polymerized in an organic solvent which cannot dissolve the polymers to precipitate granular polymers. The latter polymerization process has advantages in that concentrations of the monomers can be raised during polymerization, and the polymers can be readily separated from the solvents after polymerization, while specific catalysts and solvents must be selected.
Catalysts which can polymerize the oxirane compounds are exemplified by catalysts having actions of Lewis acids such as boron fluoride, aluminum chloride, tin chloride and iron chloride. When polymerization is carried out by using these catalysts, relatively low-molecular weight (for example, molecular weight of several thousand to around fifty thousand) polymers are obtained.
It is known to use reaction products of alkylzinc with water, reaction products of organotin compounds with phosphates, reaction products of alkylaluminum with water, reaction products of alkylaluminum with phosphoric acid compounds or the like as catalysts in order to obtain high-molecular weight polymers which are useful in specific fields such as rubber industry. In particular, as the catalysts containing alkylaluminum, catalysts prepared by adding, to the reaction products of alkylaluminum with water, further chelating agents such as acetylacetone (for example, see J. Polym. Sci. A-1, 7, 525 (1969)), catalysts prepared by adding, to the reaction products of alkylaluminum with the phosphoric acid compounds, further the third component(s) consisting of amine compounds, organophosphorus compounds and/or organoarsenic compounds (see Japanese Examined Patent Publication No. 27534/1971), catalysts prepared by adding N-substituted morpholine such as N-ethylmorpholine to the reaction products of alkylaluminum with the phosphoric acid compounds (see Japanese Examined Patent Publication No. 8852/1981) and catalysts prepared by adding 1, 8-diazabicyclo[5.4.0]-7-undecene to the above-mentioned reaction products (see Japanese Examined Patent Publication No. 51171/1981) were proposed as excellent catalysts to obtain high-molecular weight polymers of the oxirane compounds.
However, most of the above-mentioned prior arts using the alkylaluminum catalysts relate to solution polymerization. Suspension precipitation polymerization of the oxirane compounds in the presence of these catalysts caused problems that the high-molecular weight polymers sometimes are not obtained, reaction mixture cannot be stirred in a reaction apparatus and the formed polymers cannot be taken out of the reaction apparatus since the polymers does not become granular but solid.
In view of the above-mentioned various problems, objects of the present invention are to provide catalysts which exhibit excellent activities on suspension precipitation polymerization and to provide a method wherein high-molecular weight polymers of oxirane compounds can be prepared effectively in high yields in the presence of the catalysts.
Studying variously in order to solve the above-mentioned problems, the present inventors found that in catalysts prepared by adding, to reaction products of alkylaluminum compounds with oxoacid compounds of phosphorus, further the third components, only the third components having specific structure and properties give catalysts for the suspension precipitation polymerization which exhibit excellent activities to obtain the high-molecular weight polymers of the oxirane compounds, and completed the present invention.
The polymerization catalysts of the oxirane compounds according to the present invention are catalysts which are suitable to carry out the suspension precipitation polymerization of the oxirane compounds in an organic solvent which cannot dissolve the polymers and are characterized by comprising a reaction product of (A) an alkylaluminum compound, (B) an oxoacid compound of phosphorus having at least one OH group in its molecule and (C) a nitrogen-containing cyclic compound having pKa of 6 to 8.
The process for preparing the polymers of the oxirane compounds according to the present invention is a process wherein the monomeric oxirane compounds are subjected to the suspension precipitation polymerization in the organic solvent which cannot dissolve the polymers in the presence of the catalysts having the above-mentioned characteristics to prepare the polymers of the oxirane compounds.
The present invention is described in detail hereinafter.
The alkylaluminum compounds to be used in the catalysts according to the present invention are represented by the general formula:
(R7)pAlX3xe2x88x92p
wherein R7 is lower alkyl such as alkyl having one to six carbon atoms, X is halogen or hydrogen, and p is 1, 1.5, 2 or 3.
Examples of the alkylaluminum compound are triethylaluminum, diethylaluminum chloride, ethylaluminum sesquichloride [Et3Al2Cl3], triisobutylaluminum, diisobutylaluminum hydride, tri-n-butylaluminum, tri-n-propylaluminum and the like. These compounds can be used solely or in combination depending on the monomeric oxirane compounds to be used.
The oxoacid compounds of phosphorus to be used in the catalysts according to the present invention have at least one OH group in their molecules. Examples of the oxoacid compound of phosphorus are inorganic phosphoric acids such as phosphorous acid, diphosphorous acid, hypophosphorous acid, metaphosphoric acid, pyrophosphoric acid, orthophosphoric acid and polyphosphoric acid; organic phosphoric acids such as nitrilotris(methylenephosphoric acid) and 1-hydroxyethane-1, 1-diphosphonic acid; acidic phosphates, which are partially esterified products of alcohols with phosphoric acid; and the like. The acidic phosphates are represented by the general formula:
Oxe2x95x90P(OR8)q(OH)3xe2x88x92q
wherein R8 is lower alkyl such as alkyl having one to six carbon atoms, and q is 1 or 2, and they can be exemplified by acidic methyl phosphate, acidic ethyl phosphate, acidic propyl phosphate, acidic isopropyl phosphate and acidic butyl phosphate. Further, it is preferable to use, as the oxoacid compound of phosphorus, phosphoric acid or a mixture of polyphosphoric acids represented by the following general formula [II] and having a corresponding H3PO4 content of 90 to 110% by weight (compounds having a corresponding H3PO4 content of higher than 100% by weight are usually called condensed phosphoric acids), since polymerization activities of the obtained catalysts on the oxirane compounds are raised, 
wherein n is an integer of 2 to 10.
Even if the phosphoric acid or the mixture contains a small amount of moisture, it does not cause any problems, but a large amount of moisture in the phosphoric acid or the mixture inhibits catalytic reactions, and the polymerization activities tend to be lowered. Accordingly, it is preferable to use the phosphoric acid or the mixture having a corresponding H3PO4 content of 90% by weight or higher.
The nitrogen-containing cyclic compounds to be used in the catalysts according to the present invention can be compounds containing nitrogen as a member of their rings and/or compounds containing nitrogen in substituents of their rings. The nitrogen-containing cyclic compounds having pKa of 6 to 8 are compounds of which pKa values measured in aqueous solutions at 25xc2x0 C. are in the range of 6 to 8, preferably 6.2 to 7.8. Examples of such nitrogen-containing cyclic compounds are alkyl-substituted pyridines such as 2, 4, 6-trimethylpyridine, 2, 3, 6-trimethylpyridine, 2, 4-dimethylpyridine, 2, 5-dimethylpyridine, 2, 6-dimethylpyridine, 3, 5-dimethylpyridine, 4-methylpyridine, 3-ethyl-6-methylpyridine, 4-isopropylpyridine, 2-propylpyridine and 2, 3, 5, 6 -tetramethylpyridine; amino-containing pyridines such as 4-amino-3-bromomethylpyridine, 4-amino-3-bromopyridine, 2-amino-3-methylpyridine, 2-amino-4-methylpyridine, 2-amino-5-methylpyridine, 2-amino-6-methylpyridine, 2-aminopyridine, 3-aminopyridine, 3-bromo-4-(dimethylamino)pyridine, 3-bromo-4-methylaminopyridine and 4-(dimethylamino)pyridine; alkoxypyridines such as 4-ethoxypyridine and 4-methoxypyridine; N-substituted morpholines such as N-ethylmorpholine and N-methylmorpholine; substituted anilines such as N, N-diethylaniline, N-tert-butylaniline and N, N-dimethylaniline; substituted phenanthrolines such as 1, 10-dimethoxy-3, 8-dimethyl-4, 7-phenanthroline and 1, 2, 3, 8, 9, 10-hexamethyl-4, 7-phenanthroline; substituted imidazoles such as 1-methylimidazole and 4-methylimidazole; substituted toluidines such as N, N-diethyl-o-toluidine and N, N-dimethyl-p-toluidine; substituted pyrrolines such as 2-cyclohexyl-2-pyrroline and 2-ethyl-2-pyrroline; 1-aminoisoquinoline, 2-aminoquinoline, N-(2-aminoethyl)piperidine, N-(2-aminoethyl)pyrrolidine, 4-chloro-2-nitrophenol and the like. A preferred nitrogen-containing cyclic compound is a compound selected from the group consisting of the alkyl-substituted pyridines, the alkoxypyridines, the substituted phenanthrolines, the substituted toluidines, the substituted pyrrolines, N-(2 -aminoethyl)piperidine and N-(2-aminoethyl)pyrrolidine. Further, it is preferable to use the alkyl-substituted pyridines represented by the following general formula [I] as the nitrogen-containing cyclic compounds having pKa of 6 to 8, since catalytic activities and molecular weights of the obtained polymers of the oxirane compounds increase, 
wherein R1, R2, R3, R4 and R5, being the same or different, are hydrogen or lower alkyl such as alkyl having one to six carbon atoms.
Examples of the alkyl-substituted pyridine represented by the general formula [I] are 2, 4, 6-trimethylpyridine, 2, 3, 6-trimethylpyridine, 2, 4-dimethylpyridine, 2, 5-dimethylpyridine, 2, 6-dimethylpyridine, 3, 5-dimethylpyridine, 4-methylpyridine, 3-ethyl-6-methylpyridine, 4-isopropylpyridine, 2-propylpyridine, 2, 3, 5, 6-tetramethylpyridine and the like. Preferred alkyl-substituted pyridines are pyridines substituted by alkyl at least at the 2- and/or 6-position. A particularly preferred compound is 2, 4, 6-trimethylpyridine.
When the alkylaluminum compound, the oxoacid compound of phosphorus and the nitrogen-containing cyclic compound are reacted one another to synthesize the catalyst of the present invention, a mixing proportion of the nitrogen-containing cyclic compound is preferably 0.01 to 0.5 mole, more preferably 0.03 to 0.25 mole to one mole of the alkylaluminum compound. A mixing proportion of the oxoacid compound of phosphorus is appropriately selected depending on an OH number in its molecule and is preferably 0.01 to 2 moles to one mole of the alkylaluminum compound, more preferably in the molar range such that a total OH number is 0.6 to 1.2 to one mole of the alkylaluminum compound. When the mixing proportions deviate from these ranges, the polymerization activities of the resulting catalysts on the oxirane compounds tend to be lowered.
Reaction order of these three starting materials is not limited. First, the alkylaluminum compound can be reacted with the oxoacid compound of phosphorus, and then this reaction mixture can be reacted with the nitrogen-containing cyclic compound. Alternatively, first, the alkylaluminum compound can be reacted with the nitrogen-containing cyclic compound, and then this reaction mixture can be reacted with the oxoacid compound of phosphorus. There is no great difference in the polymerization activities of the obtained two catalysts on the oxirane compounds. Reaction temperatures of the above-mentioned reactions are appropriately selected depending on the alkylaluminum compounds or the oxoacid compounds of phosphorus to be used and are usually in the range of xe2x88x9220xc2x0 to 120xc2x0 C. It is preferable to carry out the reactions to synthesize the catalysts under an atmosphere of an inert gas such as a nitrogen gas without solvent or in an inert solvent. The inert solvent is not limited and can be exemplified by aliphatic hydrocarbons such as hexane, heptane, cyclohexane and octane; aromatic hydrocarbons such as benzene, toluene and xylene; ethers such as diethyl ether, dipropyl ether, methyl butyl ether and dimethoxyethane; and the like. These solvents are used solely or as mixed solvents.
The catalysts obtained by reacting the alkylaluminum compounds with the oxoacid compounds of phosphorus and the nitrogen-containing cyclic compounds are very suitable for the suspension precipitation polymerization of the oxirane compounds. Examples of polymerable oxirane compounds are alkylene oxides such as ethylene oxide, propylene oxide, butene oxide, isobutylene oxide and butadiene monoxide; substituted alkylene oxides such as epichlorohydrin, epibromohydrin, methacryl chloride oxide, trifluoromethylethylene oxide, dichloroisobutylene oxide and styrene oxide; alicyclic epoxides such as cyclohexene oxide and vinylcyclohexene oxide; glycidyl ethers such as allyl glycidyl ether, phenyl glycidyl ether, chloroethyl glycidyl ether, methyl glycidyl ether, 2-methoxyethyl glycidyl ether, 2-(2-methoxyethoxy)ethyl glycidyl ether, cyclohexyl glycidyl ether and benzyl glycidyl ether; glycidyl esters such as glycidyl acrylate and glycidyl methacrylate; and the like. It is preferable to carry out homopolymerization of the oxirane compounds represented by the following general formula [III] or copolymerization of two or more compounds among them, because polymerization rates and molecular weights of the resulting polymers increase, 
wherein m is 0 or 1, R6 is hydrogen, or alkyl, cycloalkyl, phenyl, aralkyl, alkenyl or (meth)acryloyl which can have substituent(s), and the substituent is halogen, methoxy, ethoxy or methoxyethoxy.
The polymerization process according to the present invention is a process wherein the monomeric oxirane compounds are subjected to the suspension precipitation polymerization in the presence of the above-mentioned catalysts in an organic solvent which is inert on the monomers and does not dissolve the resulting polymers to prepare the polymers of the oxirane compounds.
The monomers can be both soluble and insoluble in the organic solvent and are preferably at least partly soluble in the solvent. Examples of such solvents are aliphatic hydrocarbons such as hexane, heptane, cyclohexane and octane; aromatic hydrocarbons such as benzene, toluene and xylene; ethers such as diethyl ether, dipropyl ether, methyl butyl ether and dimethoxyethane; and the like. The solvent is appropriately selected depending on the oxirane compounds to be used and polymerization temperature. The aliphatic hydrocarbons are preferably used.
Mixing proportions of the monomeric oxirane compound, the organic solvent and the catalyst are usually preferably in the ranges of 100 to 1000 parts by weight of the organic solvent and 0.01 to 5 parts by weight of the catalyst to 100 parts by weight of the oxirane compound. The polymerization temperature is not limited, is usually in the range of xe2x88x9220xc2x0 to 150xc2x0 C. and is appropriately selected depending on activities of the catalysts and, the organic solvents and the oxirane compounds to be used. The polymerization is usually carried out with stirring.